Mário Luís Garbin

Key message: A warm, high-VPD climatic scenario revealed population-level differences in ecophysiological responses in Myrsine coriacea , highlighting contrasting responses to changing climatic conditions. Temperature and atmospheric evaporative demand are key drivers of tree performance, while phenotypic plasticity and population-level differentiation shape responses to environmental variation. In tropical montane ecosystems, understanding how populations can physiologically respond to variation in temperature and atmospheric evaporative demand is essential for predicting forest responses to climate change. We investigated the responses of Myrsine coriacea populations along an elevational gradient in the Brazilian Atlantic Forest under contrasting climatic scenarios. Seedlings from seven populations (639–1774 m a.s.l.) were grown in a common garden experiment under Cold-Dry and Warm-Humid scenarios. We evaluated growth, gas exchange, chlorophyll fluorescence, and biochemical traits to assess variation in physiological responses among populations. Low- and mid-elevation populations maintained growth under the warmer, higher-VPD scenario, whereas the highest-elevation population showed increased mortality. Although photosynthetic capacity increased under the warmer scenario, respiratory costs and light compensation points also increased, indicating patterns consistent with reduced net carbon gain. In the highest-elevation population, increased intercellular CO ₂ concentration together with reduced quantum efficiency suggested that constraints on carbon assimilation were unlikely to arise solely from CO ₂ diffusion. These results demonstrate that phenotypic shifts under the warmer climatic scenario do not necessarily translate into functional resilience. The highest-elevation population exhibited coordinated morphological and physiological adjustments, but these responses were not accompanied by improved growth or survival, suggesting limited acclimation under the warmer, higher-VPD scenario. Together, these findings highlight how population-level differentiation influences photosynthetic performance, growth, and acclimation under contrasting climatic scenarios, emphasizing the importance of intraspecific variation when predicting tropical forest responses to climate change.

Using metrics from network theory allows us to understand the structural organization of epiphyte communities and identify the host trees (phorophytes) that are fundamental to their establishment. In this study, we applied ecological network metrics to examine the structure of interactions between vascular epiphytes and phorophytes in a woody inselberg community in southeastern Brazil. The recorded network comprised 30 epiphyte species and 13 phorophyte species, exhibiting a nested structure, low specialization (H₂′), low connectance, and low modularity, like other epiphyte–phorophyte networks. The main roles in the network were played by the generalist epiphyte Tillandsia loliacea and the lithophytic phorophytes Tabebuia reticulata and Pseudobombax petropolitanum, which interacted with 100% of the recorded epiphytic species. Epiphyte species were organized vertically into modules that correlate with the ecological zones of the phorophytes, suggesting that their distribution responds to microclimatic variation along the vertical gradient. These results reinforce the importance of particular phorophyte species as key structuring agents of epiphytic communities and highlight their central role in extreme environments such as inselbergs.

Questions: Drought events are increasingly frequent, threatening the biodiversity of tropical forests. The understorey comprises a large fraction of the total plant species richness of these systems with the presence of highly diverse angiosperm families. Here, we quantified the effects of a drought on abundance and functional structures and on the ecosystem functioning of Rubiaceae assemblages along a topographic gradient.Location: Mata das Flores State Park, an Atlantic Forest fragment in southeast Brazil.Methods: Two vegetation surveys were performed: one during an El Niño‐induced drought, and the other three years after this drought. Abundance and functional structures were assessed using the 16 most‐abundant species of Rubiaceae, which comprised 92% of the total abundance. A litter decomposition experiment was carried out to estimate the percentage of mass loss by the Rubiaceae species. We carried out Procrustes analyses on abundance and functional structures and used Generalized Linear Mixed Models to test the effects of drought and topographic habitats on taxonomic and functional compositions, and mass loss.Results: We found that the functional structure and mass loss remained constant despite significant changes in the abundance structure after the drought.Conclusion: The evidence points to the maintenance of ecosystem functioning through functional redundancy, because functionally similar less‐abundant species replaced each other after the drought. We show that swarms of species can maintain biological diversity and stability in ecosystem functioning under drought in the understorey of a tropical forest.

Question: Drought‐induced tree mortality has been documented in forests worldwide but the mechanisms related to drought recovery are still poorly understood. To better predict forest trajectories under future climate scenarios, it is essential to disentangle physiological mechanisms underlying plant mortality caused by El Niño droughts. Here, we assessed how vegetation structure, vapor pressure deficit (VPD), and functional traits interact to mediate tree mortality after a severe drought in a tropical forest.Location: Mata das Flores State Park, an Atlantic Forest fragment in southeast Brazil.Methods: We established 20 permanent plots with contrasting vegetation structure and topography. In each plot, we measured tree abundance and diameter at breast height (DBH) of every woody plant (1–10 cm diameter) at the end of the drought, and two years after the break of drought, to calculate mortality rates during drought recovery. Hydraulic (e.g., maximum stomatal conductance to water vapor, stomatal density, etc.) and economic traits (specific leaf area, wood density, etc.) were measured on the 10 most abundant species. We also measured local air temperature and air humidity using HOBO dataloggers in each plot to calculate the VPD.Results: The studied Atlantic Forest understorey did not recover from the 2014–2016 drought, in terms of tree mortality. Lower VPD, driven by big trees in the valley, protected understorey plants with acquisitive economic attributes and conservative hydraulic attributes against mortality. On the other hand, higher VPD, driven by smaller trees and higher stem density on the ridge and slope, increased the mortality of understorey plants with acquisitive attributes.Conclusion: Ridges represent the most important fraction of the Atlantic Forest and our results suggest this type of forest is at high climate risk due to global change. Altogether, our results highlight that valleys are microclimate refuges for understorey plants and might help mitigate drought impacts in tropical forest under forecasted climate changes.

Plants exhibit phenotypic plasticity in response to environmental variations, which can lead to stable genetic and physiological adaptations if exposure to specific conditions is prolonged. Myrsine coriacea demonstrates this through its ability to thrive in diverse environments. The objective of the article is to investigate the adaptive responses of M. coriacea by cultivating plants from seeds collected at four different altitudes in a common garden experiment. Through integrated physiological and proteomic analyses, we identified 170 differentially accumulated proteins and observed significant physiological differences among the populations. The high-altitude population (POP1) exhibited a unique proteomic profile with significant down-regulation of proteins involved in carbon fixation and energy metabolism, suggesting a potential reduction in photosynthetic efficiency. Physiological analyses showed lower leaf nitrogen content, net CO ₂ assimilation rate, specific leaf area, and relative growth rate in stem height for POP1, alongside higher leaf carbon isotopic composition ( δ13C ) and leaf carbon ( C ) content. These findings provide insight into the complex interplay between proteomic and physiological adaptations in M. coriace a and underscore the importance of local adaptations. This study enhances our understanding of how altitude-specific selection pressures can shape plant molecular biology and physiology, offering valuable perspectives for predicting plant responses to global environmental changes. Highlight: This study unveils proteomic and physiological adaptations in a high-altitude M. coriacea population with reduced carbon fixation and energy metabolism.

Question: Individual plants of some highly diverse angiosperm families occur in aggregated spatial patterns in tropical plant communities, which have been defined as species swarms. Although this spatial aggregation seems paradoxical, because related species should segregate in space owing to expected ecological similarities, it has yet to be tested. We assessed whether species of the family Rubiaceae segregate in space in the understorey of a tropical plant community.Location: An Atlantic Forest fragment in southeast Brazil.Methods: We surveyed all local aggregates of Rubiaceae species within an 18.75‐ha plot across a topographic gradient. Based on the species abundance distribution, we used the 10 most abundant species to model their spatial patterns using univariate and bivariate spline spatial correlations. Bubble graphs were used to show how these species were distributed across the gradient.Results: A total of 12,258 individuals of 47 species were found distributed in 543 local aggregates. The 10 studied species corresponded to 86% of the total abundance and were aggregated in space, at distances from 0 to 10–300 m. Pairwise comparisons revealed a segregation pattern at scales ranging from 0 to 10–230 m. Local aggregates were strongly dominated by a single species, whereas many other species occurred at very low abundances.Conclusion: The studied species of Rubiaceae shared the understorey environment by occupying different portions of available space. Habitat preferences, negative interactions, dispersal limitation and priority effects may explain the observed spatial patterns. Swarms are not paradoxical because species of Rubiaceae use different microhabitats within the forest understorey.

Congeneric species have similarities in phenotypic and ecological traits. The sympatry of congeneric species constitutes an opportunity for studies on coexistence. Two bird species of Mimidae, the native Tropical mockingbird, Mimus gilvus Oberholser, 1919, and the restinga invader Chalk-browed mockingbird, Mimus saturninus (Lichtenstein, 1823), currently occur in sympatry across the sandy-coastal ecosystem (restinga) of Espírito Santo state, Southeastern Brazil. We studied the spatial distribution of Tropical mockingbird and Chalk-browed mockingbird to understand the degree of competition across a preserved and urban gradient. We sampled 1,451 sampling units across a preserved and urban landscape in a coastal area of southeastern Brazil. The best-fitting model for abundance (Punctual Abundance Index) included urbanization index, distance from the coast, and distance from the closest protected area, which explained 63% and 97% of the abundance of Tropical mockingbird and Chalk-browed mockingbird, respectively. The species exhibited a segregated spatial pattern at small scale, indicating that both species are avoiding one another. Chalk-browed mockingbird showed ecological plasticity in modified environments, whereas Tropical mockingbird was more sensitive to urbanization. We suggested that the coexistence of these species is associated with resource partitioning. Monitoring Tropical mockingbird populations may be a proxy for the assessment of habitat quality and restoration success in the highly threatened restinga ecosystem.